GMAT数学，掌握基本概念很重要
<p> 1 <span word="mode">mode</span> 一堆数中出现频率最高的一个或几个数 </p><p> 一堆数中出现频率最高的一个或几个数</p><p> 2.<span word="range">range</span></p><p> 一堆数中最大和最小数之差</p><p> 3.<span word="mean">mean</span></p><p> <span word="arithmatic">arithmatic</span> <span word="mean">mean</span></p><p> <span word="geometric">geometric</span> <span word="mean">mean</span> <span word="n">n</span>个数之积的<span word="n">n</span>次方根</p><p> 4.<span word="median">median</span></p><p> 将一堆数排序之后，正中间的一个数， 或者中间两个数的平均数/2=6 )</p><p> 5.<span word="standard">standard</span> <span word="error">error</span></p><p> 一堆数中，每个数与平均数的差的绝对值之和，除以这堆数的个数<span word="e">e</span>.<span word="g">g</span>. <span word="standard">standard</span> <span word="error">error</span> <span word="of">of</span> 0,2,5,7,6 <span word="is">is</span>: /5=2.4 )</p><p> 6.<span word="standard">standard</span> <span word="variation">variation</span></p><p> 一堆数中，每个数与平均数之差的平方之和，再除以<span word="ne">ne</span>.<span word="g">g</span>. <span word="standard">standard</span> <span word="variation">variation</span> <span word="of">of</span> 0,2,5,7,6 <span word="is">is</span>:_ 2 2 2 2 2_|_ ++++_|/5=6.8</p><p> 7.<span word="standard">standard</span> <span word="deviation">deviation</span></p><p> 就是<span word="standard">standard</span> <span word="variation">variation</span>的平方根</p><p> 标准方差的公式：<span word="d">d</span>^2=/<span word="n">n</span></p><p> <span word="d">d</span> 为标准方差</p><p> 8. 三角形 余玄定理<span word="C">C</span>^2=<span word="A">A</span>^2+<span word="B">B</span>^2-2<span word="ABCOSt">ABCOSt</span> <span word="t">t</span>为<span word="AB">AB</span>两条线间的夹角</p><p> 9. <span word="Y">Y</span>=<span word="k">k</span>1<span word="X">X</span>+<span word="B">B</span>1,<span word="Y">Y</span>=<span word="k">k</span>2<span word="X">X</span>+<span word="B">B</span>2，两线垂直的条件为<span word="K">K</span>1<span word="K">K</span>2=-1</p><p> 10. 熟悉一下根号2、3、5的值</p><p> <span word="sqrt">sqrt</span>=1.414 <span word="sqrt">sqrt</span>=1.732</p><p> <span word="sqrt">sqrt</span>=2.236 <span word="sqrt">sqrt</span>=3.162</p><p> 11. <span word="a">a</span> <span word="if">if</span> <span word="only">only</span> <span word="b">b</span>: <span word="b">b</span>-<span word="a">a</span></p>
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